Damper of washing machine

ABSTRACT

A damper includes: a cylinder; a piston rod disposed to be movable linearly in the cylinder; and a plurality of damping members installed between the cylinder and the piston rod, and generating a damping force by multi-stage so that when a vibration transmitted from the cylinder to the piston rod or from the piston rod to the cylinder is big, a strong damping force is generated, whereas when a vibration is small, a weak damping force is generated. A damping force is generated by stages depending on a displacement of a vibration transferred from the cylinder to the piston or from the piston to the cylinder. If a small amount of vibration is transferred, a weak damping force is generated, whereas if a large amount of vibration is transferred, a strong damping force is generated. Accordingly, a vibration damping performance can be improved.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention The present invention relates a damper of a washing machine and, more particularly, to a damper capable of enhancing a vibration damping capability by exerting a strong damping force when a vibration is severe and exerting a weak damping force when a vibration is small.

[0002] 2. Description of the Background Art

[0003]FIG. 1 is a sectional view of a general drum washing machine.

[0004] As shown in FIG. 1, the general drum washing machine includes a cabinet 2 forming the exterior, a tub 4 disposed inside the cabinet 2 and storing washing water, a drum 6 rotatably disposed inside the tub 4 and performing a washing and dewatering operation on the laundry; and a driving motor 10 disposed at a rear side of the tub 4, and connected to the drum 6 by a driving shaft 8 to rotate the drum 6.

[0005] An inlet 12 is formed at a front side of the cabinet 2 to allow the laundry to be put in or taken out therethrough, and a door 14 is provided at a front side of the inlet 12 to open/close the inlet 14.

[0006] The tub 4 communicates with the inlet 12 of the cabinet 2. A plurality of support springs 16 are installed between the upper portion of the tub 4 and an upper inner wall of the cabinet 2 and a plurality of dampers 18 are installed at a lower portion of the tub 4 and a lower inner wall of the cabinet 2 are installed so as to reduce vibration transferred to the cabinet 2 after being generated from the tub 4.

[0007]FIG. 2 is a sectional view of a damper of the washing machine in accordance with the conventional art. The damper 18 of the washing machine in accordance with the conventional art includes a cylinder 20 mounted at an outer circumferential surface of the tub 4, a piston rod 22 inserted to be linearly movable in the cylinder 20 and mounted at a bottom surface of the cabinet 2, and a friction member 24 fixed at an outer circumferential surface of the piston rod 22 and perform a damping operation by rubbing against the inner circumferential surface of the cylinder 20.

[0008] A hinge connection unit 24 hinged at an outer circumferential surface of the tub 4 is formed at an upper end of the cylinder 20, and the lower end of the cylinder 20 is opened so that the piston rod 22 can be inserted thereinto, and a guide bush 26 is installed at an inner circumferential surface of the opened lower end so that the piston rod 22 can be movable linearly.

[0009] An insertion groove 28 is formed at an upper end of the piston rod 22, so that the friction member 24 can be insertedly fixed, and a hinge connection unit 30 is formed at a lower end of the piston rod 22 and hinged at the bottom surface of the cabinet 2.

[0010] The damper 18 of the washing machine in accordance with the conventional art is functioned such that when a vibration takes place from the tub 4, the friction member 24 rubs on the inner circumferential surface of the cylinder 20, thereby generating a damping force to damp a vibration.

[0011] However, as for the conventional damper, if a frictional force generated from the friction member is set strong, the friction member would not rub on the inner circumferential surface of the cylinder, failing to generate a damping force. Then, the vibration of the tub is transferred as it is to the cabinet, increasing a noise and a vibration of the washing machine.

[0012] Meanwhile, if the friction force generated from the friction member is set weak, when a large amount of vibration takes place, a damping force of the friction member is reduced, failing to enough support the tub to be dampable. Thus, a performance of the washing machine is weakened, and a large amount of vibration is generated.

SUMMARY OF THE INVENTION

[0013] Therefore, an object of the present invention is to provide a damper for a washing machine capable of enhancing a vibration damping performance by generating a weak damping force when a small amount of vibration is received, and a strong damping force when a large amount of vibration is received.

[0014] To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a damper for a washing machine including: a cylinder connected to one of a tub and a cabinet; a piston rod connected to the other remaining one of the tub and the cabinet; and a damping unit installed between the cylinder and the piston rod and generating a damping force in a multi-step to exert a weak damping force when vibration transferred from the cylinder to the piston rod or from the piston rod to the cylinder is small and exerting a strong damping force when vibration transferred from the cylinder to the piston rod or from the piston rod to the cylinder is small is big.

[0015] The damping unit includes a first damping member mounted at the piston rod and elastically deformed to generate a damping force when a relatively small vibration is generated; and a second damping member mounted at an outer circumference of the first damping member and generating a damping force by rubbing on the inner circumferential surface of the cylinder when a relatively big vibration is generated.

[0016] The first damping member is made of a material having an elastic force, of which an inner circumferential surface is insertedly fixed at an engaging unit formed at the piston rod and both sides are disposed to maintain a certain interval from the inner side of the engaging unit formed at the piston rod.

[0017] The first damping member is made of a rubber material elastically deformed when a vibration transferred from the cylinder to the piston rod or from the piston rod to the cylinder is smaller than a first displacement value.

[0018] The second damping member is made of a grease-absorbed sponge material.

[0019] The damping unit includes: a first damping member mounted at the piston rod and exerting a damping force when a vibration smaller than a first displacement value is generated; a second damping member mounted at an outer circumference of the first damping member and exerting a damping force when a vibration equal to or greater than the first displacement value but smaller than a second displacement value is generated; and a third damping member mounted at an outer circumference of the second damping member and exerting a damping force when a vibration equal to or greater than the second displacement value is generated.

[0020] The damping unit includes: a connection rod connected to a lower end of the piston rod; a first damping member fixed at the center of a connection rod and generating a damping force by being elastically deformed when a vibration smaller than a pre-set value is transferred; and a second damping member mounted at both ends of the first damping member, tightly attached to a friction surface of the cylinder in a rubbing-available manner, and generating a damping force by rubbing on the friction surface when a vibration greater than the pre-set value is transferred.

[0021] The damping unit includes a first coil spring-type damping member connected to a lower end of the piston rod and generating a damping force when a vibration smaller than a pre-set value is generated; a support bar for supporting one end of the other side of the first damping member; and a second damping member insertedly coupled to both ends of the support bar and tightly attached to the friction surface of the cylinder in a rubbing-available manner.

[0022] The damping unit includes: a connection rod fixed at a lower end of the piston rod; a support member into which the connection rod is inserted to be movable linearly; a first damping member formed as first coil spring and second coil spring supported between the support member and the connection rod and exerting a damping force when a vibration smaller than a pre-set value is generated; and a second damping member fixed at both ends of the support member and generating a damping force by rubbing on the friction surface of the cylinder when a vibration greater than the pre-set value is generated.

[0023] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

[0025] In the drawings:

[0026]FIG. 1 is a sectional view showing a general drum washing machine;

[0027]FIG. 2 is a sectional view showing a damper for a washing machine in accordance with a conventional art;

[0028]FIG. 3 is a sectional view showing a damper in accordance with a first embodiment of the present invention;

[0029]FIG. 4 is an enlarged view of a portion ‘A’ of FIG. 3;

[0030]FIGS. 5 and 6 show operational states of the damper in accordance with the first embodiment of the present invention;

[0031]FIG. 7 is a sectional view showing a damper in accordance with a second embodiment of the present invention;

[0032]FIG. 8 is an enlarged view of a portion ‘B’ of FIG. 7;

[0033] FIGS. 9 to 11 show operational states of the damper in accordance with the second embodiment of the present invention;

[0034]FIG. 12 is a sectional view of a damper in accordance with a third embodiment of the present invention;

[0035]FIGS. 13 and 14 are views showing operation states of the damper in accordance with the third embodiment of the present invention;

[0036]FIG. 15 is a sectional view showing a damper in accordance with a fourth embodiment of the present invention;

[0037]FIGS. 16 and 17 are views showing operation states of the damper in accordance with the fourth embodiment of the present invention;

[0038]FIG. 18 is a sectional view showing a damper in accordance with a fifth embodiment of the present invention; and

[0039]FIGS. 19 and 20 are views showing operation states of the damper in accordance with the fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0041] A drum washing machine in accordance with preferred embodiments will now be described with reference to the accompanying drawings.

[0042]FIG. 3 is a sectional view showing a damper in accordance with a first embodiment of the present invention.

[0043] With reference back to FIG. 1, the washing machine in accordance with the present invention includes: includes a cabinet 2 forming an exterior, a tub 4 disposed inside the cabinet 2 and storing washing water, a drum 6 rotatably disposed inside the tub 4 and performing a washing and dewatering operation on the laundry. In addition, the washing machine of the present invention also includes a plurality of support springs 16 installed between an upper portion of the tub 4 and an upper inner wall of the cabinet 2, and a plurality of dampers installed between a lower portion of the tub 4 and a lower inner wall of the cabinet 2, to thereby reduce the vibration transferred to the cabinet after being generated from the tub 4.

[0044] The damper 50 in accordance with a first embodiment of the present invention includes: a cylinder 52 mounted at an outer circumferential surface of the tub 4; a piston rod 54 mounted at a bottom surface of the cabinet 2; and a damping unit mounted at the piston rod 54 and exerting a weak damping force when a relatively small vibration is generated and exerting a strong damping force when a relatively big vibration is generated.

[0045] The damping unit includes a first damping member 56 for exerting a damping force when a vibration smaller than a pre-set value is transferred and a second damping member 58 mounted at an outer circumference of the first damping member 56 and exerting a damping force when a vibration greater than the pre-set value is generated.

[0046] The cylinder 52 has a hinge connection unit 62 formed at its upper side and hinged at an outer circumferential surface of the tub 4, and a friction face 72, 15 on which the second damping member 58 rubs, formed at its inner circumferential surface. A lower end of the cylinder 52 is opened so that the piston rod 54 can be inserted thereinto, and a ring type guide bush 66 for guiding the piston rod 54 to be movable linearly is installed at an inner circumferential surface of the lower end of the cylinder 52.

[0047] At a lower side of the piston rod 54, there is provided a hinge connection unit 64 which is hinged at a bottom surface of the cabinet 2, and at an upper side thereof, an engaging unit 68 is formed dug down with a predetermined depth in a circumferential direction, so that the first damping member 56 can be coupled thereto.

[0048] The engaging unit 68 is formed with a diameter smaller than that of the piston rod 54, and both sides of the engaging unit 68 include a sloping side 70 having a predetermined tilt angle (θ2).

[0049] The first damping member 56 is insertedly coupled to the engaging unit 68, so that when a small amount of vibration is transferred to the cylinder 52, the first damping member 56 is elastically deformed by itself to perform a damping operation. The second damping member 58 is coupled at the outer circumferential surface of the first damping member 56, so that when a large amount of vibration is transferred to the cylinder 52, the second damping member 58 rubs on the friction face 72 of the cylinder 52 for a damping operation. A support member 60 is installed between the first damping member 56 and the second damping member 58 so as to fix the second damping member 58 at the outer circumferential surface of the first damping member 56.

[0050] The first damping member 56 will now be described in detail.

[0051] The first damping member 56 is made of a material having a certain elastic force and includes a through hole 74 formed at its inner circumferential surface, so that the engaging unit 68 is insertedly coupled thereto, and a groove 76 formed in a circumferential direction at its outer circumferential surface, into which the support member 60 is inserted.

[0052] The side of the first damping member 56 includes a sloping side 78 having a tilt angle (θ1) with a width widening as it goes outside. The tilt angle (θ1) of the sloping side 78 of the first damping member is smaller as much as a predetermined angle (θ3) than the tilt angle (θ2) of the sloping side 70 of the engaging unit 68, so that the side of the first damping member 56 is positioned at a certain interval from the engaging unit 68.

[0053] The first damping member 56 is preferably made of a rubber material and has a predetermined elastic force so as to be elastically deformed when a vibration smaller than a first displacement value (d) takes place from the cylinder 52.

[0054] The second damping member 58 is formed in a circular ring type, of which an inner circumferential surface is insertedly fixed at the support member 60 and an outer circumferential surface is disposed to rub on the friction surface 72 of the cylinder 52.

[0055] The second damping member 58 is preferably made of a sponge material with grease absorbed therein. If a vibration transferred to the cylinder 52 is smaller than the first displacement value, the second damper member 58 is maintained in a tightly attached to the friction surface of the cylinder 52. If, however, a vibration transferred to the cylinder 52 is equal to or greater than the first displacement value (d), the second damper member 58 rubs on the friction surface 72 of the cylinder 52, generating a damping force.

[0056] The support member 60 has a ring type and includes a holing protrusion 80 formed at its inner circumferential surface and inserted into the groove 76 formed at the outer circumferential surface of the first damping member 56 and a fixing groove 82 formed at its outer circumferential surface and fixing the second damping member.

[0057] The operation of the damper of the washing machine constructed as described will now be explained.

[0058]FIGS. 5 and 6 show operational states of the damper in accordance with the first embodiment of the present invention.

[0059] First, when the washing machine is driven, a vibration taking place at the tub 4 according to rotation of the drum 6 is transferred to the cylinder 52. At this time, if the vibration transferred to the cylinder 52 is smaller than the first displacement value (d), as shown in FIG. 5, the second damping member 58 is maintained in the state of being tightly attached to the inner circumferential surface of the cylinder 52, and in this state, the sloping side 78 is elastically deformed as much as a predetermined width (D1) to generate a damping force. Accordingly, the vibration smaller than the first displacement value (D1) generated from the tub 4 is damped and transferred to the cabinet.

[0060] During the operation, if a large amount of vibration having a second displacement value (D2) which is greater than the first displacement value (D1), takes place and is transferred to the cylinder 52 owing to a washing operation of the washing machine, as shown in FIG. 6, it exceeds a limitation of the elastic deformation of the first damper member 56, and in this case, the second damping member 58 rubs on the friction face 72 to generate a damping force to damp transfer of the large amount of vibration of the tub to the cabinet. Herein, the second displacement value D2 is tantamount to the sum of the deformed width (D1) of the first damper member 56 and the distance (D3) as long as the second damping member rubs.

[0061]FIG. 7 is a sectional view showing a damper in accordance with a second embodiment of the present invention, and FIG. 8 is an enlarged view of a portion ‘B’ of FIG. 7.

[0062] A damper 90 in accordance with the second embodiment of the present invention includes a cylinder 52 mounted at an outer circumferential surface of the tub 4, a piston rod 54 mounted at a bottom surface of the cabinet 2, a first damping member 92 mounted at the piston rod 54 and generating a damping force when a vibration smaller than a first displacement value (P1) takes place; a second damping member 94 disposed at an outer circumferential surface of the first damping member 92 and generating a damping force when a vibration equal to or greater than the first displacement value (P1) but smaller than a second displacement value (P2) takes place; and a third damping member 96 disposed at an outer circumferential surface of the second damping member 94 and generating a damping force when a vibration equal to or greater than the second displacement value (P2) takes place.

[0063] An engaging unit 68 is formed at the piston rod 54, to which the first damping member 92 is insertedly fixed, and both sides of the engaging unit 68 has a sloping side 70 with a predetermined tilt angle (θ4).

[0064] The first damping member 92 is insertedly coupled at the engaging unit 68 formed at the piston rod 54. A first support member 98 is fixed at an outer circumferential surface of the first damping member 92. The second damping member 94 is fixed at an outer circumferential surface of the first support member 98. A second support member 100 is fixed at an outer circumferential surface of the second damping member 94. The third damping member 96 is fixed at an outer circumferential surface of the second support member 100 and rubs on the friction face 72 of the cylinder 52.

[0065] The first damping member 92 is made of a material having an elastic force by itself, of which an inner circumferential surface is insertedly coupled at the engaging unit 68 of the piston rod 54 and an outer circumferential surface is fixed at the first support member 98.

[0066] The side of the first damping member 92 has a sloping side 108 having a tilt angle (θ5) with a width widening as it goes toward outside. The tilt angle (θ5) of the sloping side 108 of the first damping member 92 is smaller than the tilt angle (θ4) of the sloping side 70 of the engaging unit 68, so that the side of the first damping member 92 is positioned at a certain interval from both sides of the engaging unit 70.

[0067] The first support member 98 having a cylindrical shape includes a first engaging protrusion 102 formed at its inner circumferential surface and insertedy fixed to an outer circumferential surface of the first damping member 92 and a second engaging protrusion 105 formed at its outer circumferential surface and insertedly fixed to the inner circumferential surface of the second damping member 94.

[0068] The second damping member 94 is fixed between the first and second support members 98 and 100, and its side is formed as a sloping side 106 having a predetermined tilt angle (θ6).

[0069] The second support member 100 has a sloping side 110 formed at its inner circumferential surface and having a tilt angle (θ7) greater than the tilt angle (θ6) of the sloping side of the second damping member 94, and a mounting groove 112 formed at its outer circumferential surface to allow the third damping member 96 to be fixed therein.

[0070] The first damping member 92 and the second damping member 94 are made of rubber, and the second damping member 94 has a greater elastic force than that of the first damping member 92.

[0071] Referring to the third damping member 96, its inner circumferential surface is insertedly fixed to the second support member 100 and its outer circumferential surface is disposed to rub against the friction face 72 of the cylinder 52. The third damper member 96 is made of a sponge material with grease absorbed therein.

[0072] The operation of the damper in accordance with the second embodiment of the present invention constructed as described above will now be explained.

[0073] FIGS. 9 to 11 show operational states of the damper in accordance with the second embodiment of the present invention.

[0074] First, when a vibration taking place from the tub 4 is transferred to the cylinder and if the vibration is smaller than the first placement (P1), as shown in FIG. 9, the first damping member 92 is elastically deformed as much as a predetermined displacement value (T) in a state of being fixed in the engaging groove 68 of the piston rod, in order to generate a damping force to damp the vibration.

[0075] If a vibration equal to or greater than the first displacement value (P1) but smaller than the second displacement value (P2) takes place from the cylinder 52, as shown in FIG. 10, the first damping member 92 and the second damping member 94 are elastically deformed as much as a predetermined displacement value (T2) to generate a damping force.

[0076] If the displacement value (P3) greater than the second displacement value (P2) takes place from the cylinder 52, as shown in FIG. 11, the first damping member 92 and the second damping member 94 are elastically deformed as much as the displacement value (T2) to generate a damping force and the second damping member 96 rubs on the friction face 72 of the cylinder 52 as much as the displacement value (T3) to generate a damping force to thereby damp transfer of the large amount of vibration taking place from the tub 4 to the cabinet 2.

[0077]FIG. 12 is a sectional view showing a damper in accordance with a third embodiment of the present invention.

[0078] A damper in accordance with the third embodiment of the present invention includes a piston rod 54 mounted at an outer circumferential surface of the tub 4, a cylinder 52 mounted at the bottom of the cabinet 2, and a damping unit installed between the piston rod 54 and the inner circumferential surface of the cylinder 52 and exerting a weak damping force when a relatively small vibration occurs and exerting a strong damping force when a relatively big vibration occurs.

[0079] The damping unit includes a connection rod connected to a lower end of the piston rod 54, a first elastic member 124 fixed at a lower end of the connection rod and generating a damping force by being elastically deformed when a small vibration smaller than a pre-set value occurs, and a second damping member 128 mounted at both end portions of the first elastic member 124 and generating a damping force by rubbing on the friction surface 72 formed at the inner circumferential surface of the cylinder 52 when a vibration greater than a pre-set value is generated.

[0080] A support member 126 is fixed at both ends of the first damping member 124 and the second damping member 128 is insertedly coupled to an outer circumferential surface of the support member 126.

[0081] The first damping member 124 is formed in a plate-spring type absorbing vibration by being elastically deformed when a relatively small vibration is transferred through the piston rod 54.

[0082] The second damping member 128 is formed in a circular ring type and disposed such that its inner circumferential surface is insertedly fixed to the support member 126 and its outer circumferential surface rubs on the friction surface 72 of the cylinder 52.

[0083] Preferably, the second damper member 128 is made of a grease-absorbed sponge material. If a vibration transferred from the piston rod 54 to the cylinder 52 is smaller than the pre-set value, the second damping member 128 is maintained to be tightly attached to the friction surface of the cylinder 52, while if a vibration transferred to the piston rod 54 is greater than the pre-set value, the second damping member 128 rubs on the friction surface 72 of the cylinder 52 to generate a damping force.

[0084] The damper 120 in accordance with the third embodiment of the present invention is operated as follows.

[0085] First, a washing machine is driven and a vibration generated from the tub 4 according to rotation of the drum 6 is transferred to the piston rod 52. At this time, if the vibration is smaller than the pre-set value, as shown in FIG. 13, the second damping member 128 is maintained to be tightly attached to the inner circumferential surface of the cylinder 52 while the first damping member 124 is elastically deformed in a vertical direction by the vibration transferred through the connection rod 122 connected to the piston rod 54 to generate a damping force to absorb the vibration.

[0086] In this course, when vibration transferred to the piston rod 54 goes beyond the pre-set value due to a washing operation of the washing machine, as shown in FIG. 14, it exceeds limitation of the elastic deformation of the first damper member 124. Then, the second damping member 124 rubs on the friction surface 72 of the cylinder 52 to generate a damping force to damp the big vibration of the tub 4 transferred to the cabinet 2.

[0087]FIG. 15 is a sectional view showing a damper in accordance with a fourth embodiment of the present invention, and FIGS. 16 and 17 are views showing operation states of the damper in accordance with the fourth embodiment of the present invention.

[0088] A damper 130 in accordance with the fourth embodiment of the present invention is the same as the damper 120 of the third embodiment of the present invention, except that the damping unit has a different structure.

[0089] The damping unit in the fourth embodiment of the present invention includes a first coil-spring type damping member 132 with one end connected to a lower end of the piston rod 54 and generating a damping force when a vibration smaller than a pre-set value is generated; a support member 134 for fixing the other end of the first damping member 132; and a second damping member 136 insertedly coupled to both ends of the support member 134 and tightly attached to the friction surface 72 of the cylinder 52 in a rubbing-available manner.

[0090] The first damping member 132 in the coil-spring type is connected between an end of the piston rod 54 and the center of the support member 134 and generating a damping force when a vibration smaller than the pre-set value is transferred through the piston rod 54.

[0091] A support plate 138 is formed at both end portions of the support member 134, into which the second damping member 136 is insertedly coupled.

[0092] The damper 130 in accordance with the fourth embodiment of the present invention is operated as follows.

[0093] When a vibration smaller than the pre-set value is generated, the coil spring, the first damping member 132, is shrunken or stretched to generate a damping force as shown in FIG. 16, or when a vibration greater than the pre-set value is generated, the second damping member 136 rubs on the friction surface 72 of the cylinder 52 to generate a damping force as shown in FIG. 17.

[0094]FIG. 18 is a sectional view showing a damper in accordance with a fifth embodiment of the present invention, and FIGS. 19 and 20 are views showing operation states of the damper in accordance with the fifth embodiment of the present invention.

[0095] A damper 140 in accordance with the fifth embodiment of the present invention is the same as the damper 130 of the third embodiment of the present invention, except that the damping unit has a different structure.

[0096] The damping unit in the fifth embodiment of the present invention includes a connection rod fixed at a lower end of the piston rod 54; a support member 144 into which the connection rod 142 is inserted to be movable linearly; first damping members 146 and 148 supported between the support member 144 and the connection rod 142 and generating a damping force when a small vibration occurs; and a second damping member 150 fixed at both ends of the support member 144 and generating a damping force by rubbing on the friction surface 72 of the cylinder 52 when a big vibration occurs.

[0097] A through hole 156 is formed at the center of the support member 144 to allow the connection rod 142 to pass therethrough and be movable linearly, and first and second stoppers 158 and 160 are formed at the connection rod 142 to support the first damping members 146 and 148.

[0098] The first damping members 146 and 148 refer, respectively, to the first coil spring 146 positioned at an upper side of the support member 144, of which one end is supported by one side of the support member 144 and the other end is supported by the first stopper 158 formed at the connection rod 142, and to the second coil spring 148 positioned at a lower side of the support member 144, of which one end is supported by the other side of the support member 144 and the other end is supported by the second stopper 160 formed at the connection rod 142.

[0099] The support plate 154 is formed at both ends of the support member 144, into which the second damping member 150 is insertedly coupled.

[0100] The damper 140 in accordance with the fifth embodiment of the present invention is operated as follows.

[0101] When a vibration smaller than the pre-set value is transferred, the first coil spring 146 and the second coil spring 148 are shrunken and stretched to generate a damping force as shown in FIG. 19. Meanwhile, when a vibration greater than a pre-set value is generated, the second damping member 150 rubs on the friction surface 72 of the cylinder 52 to generate a damping force.

[0102] As so far described, the damper of the present invention has the following advantages.

[0103] That is, the damper generates a damping force by stages depending on a displacement of a vibration transferred from the cylinder to the piston or from the piston to the cylinder. Accordingly, if a small amount of vibration is transferred, a weak damping force is generated, whereas if a large amount of vibration is transferred, a strong damping force is generated. Accordingly, a vibration damping performance can be enhanced.

[0104] As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims. 

What is claimed is:
 1. A damper for a washing machine comprising: a cylinder connected to one of a tub and a cabinet; a piston rod connected to the other remaining one of the tub and the cabinet; and a damping unit installed between the cylinder and the piston rod and generating a damping force in a multi-step to exert a weak damping force when vibration transferred from the cylinder to the piston rod or from the piston rod to the cylinder is small and exerting a strong damping force when vibration transferred from the cylinder to the piston rod or from the piston rod to the cylinder is big.
 2. The damper of claim 1, wherein the damping unit comprises: a first damping member mounted at the piston rod and elastically deformed to generate a damping force when a relatively small vibration is generated; and a second damping member mounted at an outer circumference of the first damping member and generating a damping force by rubbing on the inner circumferential surface of the cylinder when a relatively big vibration is generated.
 3. The damper of claim 2, wherein the first damping member is made of a material having an elastic force, of which an inner circumferential surface is insertedly fixed at an engaging unit formed at the piston rod and both sides are disposed to maintain a certain interval from the inner side of the engaging unit formed at the piston rod.
 4. The damper of claim 3, wherein both sides of the engaging unit of the piston rod have a sloping side with a predetermined tilt angle (θ1), and the side of the first damping member has a sloping side with a tilt angle (θ2) smaller than the tilt angle (θ1) of the sloping side of the engaging unit.
 5. The damper of claim 2, wherein the first damping member is made of a rubber material elastically deformed when a vibration transferred from the cylinder to the piston rod or from the piston rod to the cylinder is smaller than a first displacement value.
 6. The damper of claim 2, wherein a support member is installed between the first damping member and the second damping member to fix the second damping member at an outer circumferential surface of the first damping member.
 7. The damper of claim 6, wherein an inner circumferential surface of the second damping member is insertedly fixed to the support member, and an outer circumferential surface of the second damping member rubs on a friction surface of the cylinder.
 8. The damper of claim 7, wherein the second damping member is made of a grease-absorbed sponge material.
 9. The damper of claim 1, wherein the damping unit comprises: a first damping member mounted at the piston rod and exerting a damping force when a vibration smaller than a first displacement value is generated; a second damping member mounted at an outer circumference of the first damping member and exerting a damping force when a vibration equal to or greater than the first displacement value but smaller than a second displacement value is generated; and a third damping member mounted at an outer circumference of the second damping member and exerting a damping force when a vibration equal to or greater than the second displacement value is generated.
 10. The damper of claim 9, wherein a first support member is fixed between the first damping member and the second damping member, and a second support member is fixed between the second damping member and the third damping member.
 11. The damper of claim 9, wherein the first damping member is formed such that its inner circumferential surface fixed at an engaging unit formed at the piston rod and its side is formed as a sloping side with a tilt angle (θ5) smaller than a tilt angle (θ4) of the sloping side of the engaging unit.
 12. The damper of claim 10, wherein the second damping member has an inner circumferential surface fixed at the outer circumferential surface of the first support member, an outer circumferential surface fixed at the second support member, and a side formed as a sloping side having a tilt angle (θ6) smaller than a tilt angle (θ7) of the sloping side of the second support member.
 13. The damper of claim 10, wherein the first and second damping members are made of a rubber material, and the third damping member is made of a grease-absorbed sponge material.
 14. The damper of claim 1, wherein the damping unit comprises: a connection rod connected to a lower end of the piston rod; a first damping member fixed at the center of a connection rod and generating a damping force by being elastically deformed when a vibration smaller than a pre-set value is transferred; and a second damping member mounted at both ends of the first damping member, tightly attached to a friction surface of the cylinder in a rubbing-available manner, and generating a damping force by rubbing on the friction surface when a vibration greater than the pre-set value is transferred.
 15. The damper of claim 14, wherein first friction member is formed in a plate-spring type which is elastically deformed to absorb a relatively small vibration transferred through the piston rod.
 16. The damper of claim 14, wherein a support member is formed at both ends of the first friction member and a second friction member is insertedly coupled to an outer circumferential surface of the support member.
 17. The damper of claim 1, wherein the damping unit comprises: a first coil spring-type damping member connected to a lower end of the piston rod and generating a damping force when a vibration smaller than a pre-set value is generated; a support bar for supporting one end of the other side of the first damping member; and a second damping member insertedly coupled to both ends of the support bar and tightly attached to the friction surface of the cylinder in a rubbing-available manner.
 18. The damper of claim 17, wherein the first damping member is formed as a coil spring having a predetermined elastic force, of which one end is fixed at the piston rod and the other end is fixed at the center of the support bar.
 19. The damper of claim 1, wherein the damping unit comprises: a connection rod fixed at a lower end of the piston rod; a support member into which the connection rod is inserted to be movable linearly; a first damping member formed as first and second coil springs supported between the support member and the connection rod and exerting a damping force when a vibration smaller than a pre-set value is generated; and a second damping member fixed at both ends of the support member and generating a damping force by rubbing on the friction surface of the cylinder when a vibration greater than the pre-set value is generated.
 20. The damper of claim 19, wherein a through hole is formed at the center of the support member to allow the connection rod to pass therethrough and be movable linearly, and first and second stoppers are formed at the connection rod to support the first damping member, and the first coil spring of the first damping member is supported between one side of the support member and the first stopper formed at the connection rod and the second coil spring of the first damping member is supported between the other side of the support member and the second stopper formed at the connection rod. 